What the Analog Value Object Is
The Analog Value object, defined in Clause 12.4 of ANSI/ASHRAE 135-2024, represents an analog value inside a BACnet device that is not tied to a physical input or output. Where an Analog Input reads a sensor and an Analog Output drives hardware, an Analog Value is a software point: a setpoint, a tuning parameter, a calculated result, or any number the control logic holds and may share.
An Analog Value can be read-only or commandable. When it is commandable, it carries the same 16-slot priority array as an Analog Output; when it is a simple stored value, it does not. Analog Value objects that support intrinsic reporting apply the OUT_OF_RANGE event algorithm.
Where You’ll See It
- Setpoints. A zone temperature setpoint an operator writes and the control loop reads is almost always an Analog Value.
- Calculated values. A computed enthalpy, a running average, or a demand total the logic exposes for other devices to read.
- Tuning parameters. PID gains, deadbands, and thresholds a technician adjusts without touching a physical channel.
Required Properties
Clause 12.4 requires every Analog Value object to provide these properties. Datatypes are the spec’s names: REAL is a floating-point number, BOOLEAN a true/false flag, and the BACnet-prefixed types are structured values defined by the standard.
| Property | Datatype | What it holds |
|---|---|---|
Object_Identifier | BACnetObjectIdentifier | The object’s type and instance number, unique within the device |
Object_Name | CharacterString | The human-readable point name, unique within the device |
Object_Type | BACnetObjectType | Always analog-value for this object |
Present_Value | REAL | The value. Read-only or commandable depending on the instance |
Status_Flags | BACnetStatusFlags | Four health flags: in-alarm, fault, overridden, out-of-service |
Event_State | BACnetEventState | The object’s current event state (normal, high-limit, low-limit, or fault for this object type) |
Out_Of_Service | BOOLEAN | When true, Present_Value is decoupled for testing and override |
Units | BACnetEngineeringUnits | The engineering units of the value |
Property_List | BACnetARRAY[N] of BACnetPropertyIdentifier | The list of properties this instance actually implements |
When the object is commandable, it additionally implements Priority_Array (the 16 command slots), Relinquish_Default (the fallback when all slots are Null), and Current_Command_Priority. On a simple stored Analog Value these are absent. See How Commanding Works on the Analog Output page for the priority-array model.
Optional Properties
The properties integrators meet most are COV_Increment, the alarm-limit group (High_Limit, Low_Limit, Deadband, Limit_Enable), and, on commandable instances, the command-tracking group. The intrinsic-reporting group generally appears or is absent as a set.
| Property | Datatype | Group |
|---|---|---|
Description | CharacterString | General |
Resolution | REAL | General |
Min_Pres_Value | REAL | Value range |
Max_Pres_Value | REAL | Value range |
Priority_Array | BACnetPriorityArray | Commanding |
Relinquish_Default | REAL | Commanding |
Current_Command_Priority | BACnetOptionalUnsigned | Commanding |
Value_Source | BACnetValueSource | Commanding |
Value_Source_Array | BACnetARRAY[16] of BACnetValueSource | Commanding |
Last_Command_Time | BACnetTimeStamp | Commanding |
Command_Time_Array | BACnetARRAY[16] of BACnetTimeStamp | Commanding |
COV_Increment | REAL | COV reporting |
Time_Delay | Unsigned | Intrinsic reporting |
Notification_Class | Unsigned | Intrinsic reporting |
High_Limit | REAL | Intrinsic reporting |
Low_Limit | REAL | Intrinsic reporting |
Deadband | REAL | Intrinsic reporting |
Limit_Enable | BACnetLimitEnable | Intrinsic reporting |
Event_Enable | BACnetEventTransitionBits | Intrinsic reporting |
Acked_Transitions | BACnetEventTransitionBits | Intrinsic reporting |
Notify_Type | BACnetNotifyType | Intrinsic reporting |
Event_Time_Stamps | BACnetARRAY[3] of BACnetTimeStamp | Intrinsic reporting |
Event_Message_Texts | BACnetARRAY[3] of CharacterString | Intrinsic reporting |
Event_Message_Texts_Config | BACnetARRAY[3] of CharacterString | Intrinsic reporting |
Event_Detection_Enable | BOOLEAN | Intrinsic reporting |
Event_Algorithm_Inhibit_Ref | BACnetObjectPropertyReference | Intrinsic reporting |
Event_Algorithm_Inhibit | BOOLEAN | Intrinsic reporting |
Time_Delay_Normal | Unsigned | Intrinsic reporting |
Reliability | BACnetReliability | Fault detection |
Fault_High_Limit | REAL | Fault detection |
Fault_Low_Limit | REAL | Fault detection |
Reliability_Evaluation_Inhibit | BOOLEAN | Fault detection |
Audit_Level | BACnetAuditLevel | Auditing |
Auditable_Operations | BACnetAuditOperationFlags | Auditing |
Tags | BACnetARRAY[N] of BACnetNameValue | Tagging and profile |
Profile_Location | CharacterString | Tagging and profile |
Profile_Name | CharacterString | Tagging and profile |
Related Objects
- Analog Input: a measured value from a physical input.
- Analog Output: a commanded value driven to physical hardware.
- Binary Value: the two-state software point (a mode flag or enable).
What Chipkin Provides
The Analog Value object, in both read-only and commandable forms, is a first-class object type in the CAS BACnet Stack. Talk to us about modeling your device’s points.